1. Field of the Invention
This invention relates to apparatus for manufacturing flat glass wherein the glass is formed while being supported on a surface of a pool of molten metal contained in a refractory lined, enclosed forming chamber. More particularly, this invention relates to a combination of structural elements for improving the quality of enclosure from the external environment provided by such an apparatus.
2. Brief Description of the Prior Art
It is known that molten glass can be delivered onto a pool of molten metal, particularly tin or a tin alloy, and thereafter cooled and attenuated to form a continuous, dimensionally stable sheet or ribbon of glass. Specific glass forming techniques and apparatus are shown and described in the following patents: U.S. Pat. No. 710,357 to Heal; U.S. Pat. No. 789,911 to Hitchcock; U.S. Pat. Nos. 3,083,551 and 3,220,816 to Pilkington; and U.S. Pat. No. 3,843,346 to Edge and Kunkle. In all of these, but Pilkington's, a stream of glass is delivered onto molten metal along a substantially horizontal path that is without free-fall pouring. Whether the path is perfectly horizontal or down a slope, the streamlines of glass flow are maintained during delivery in these methods such as exemplified by that of Edge and Kunkle. In practicing the method of Edge and Kunkle, the molten glass is preferably delivered over a refractory threshold having an uppermost surface that is at or above the level of molten metal in the associated forming chamber so that the threshold acts not only as a glass support but as a dividing wall between a furnace refiner or conditioner and its associated forming chamber. Such a threshold effectively serves as a topmost portion of a furnace front basin wall and, at the same time, as an inlet or entrance end wall of the forming chamber.
In general, a forming chamber includes an outer impervious casing, usually of steel, and an inside refractory liner. Hitchcock in U.S. Pat. No. 1,564,240 shows that the molten metal of a forming chamber may be contained in a metal casing. Exemplary patents showing refractory-lined metal casing structures are U.S. Pat. Nos. 3,584,475 and 3,594,147 to Galey and Sensi and U.S. Pat. No. 3,584,477 to Hainsfurther.
Various threshold assemblies and facilities are shown and described in the following patents: U.S. Pat. No. 3,843,344 to Galey; U.S. Pat. No. 3,854,922 to Sensi and Wehner; U.S. Pat. No. 3,898,069 to Cerutti and Gulotta; U.S. Pat. No. 3,884,665 to Edge and Kunkle and U.S. Pat. Nos. 3,843,345 and 3,928,012 to Harrell and Foster. U.S. Pat. No. 3,898,069 to Cerutti and Gulotta describes and claims a positive containment threshold that includes a vertical casing member (or cooler) along with a casing bottom extension and casing side extensions to include a part of the refractory threshold inside a bottom portion (or extension) of a forming chamber casing. It has been found that this and other forming chamber casing-liner-threshold combinations may be modified to improve their ability to isolate the interior of such forming chambers from the outside environment.
In both the forming chambers, such as described by Edge and Kunkle and those such as described by Pilkington, there is a need to isolate the interior of the chambers from the outside environment. Otherwise, the supporting molten metal might oxidize or bubbles might be introduced into the glass. See Canadian Pat. No. 878,044 to Michalik which describes the need for a protective reducing gas mixture in a glass forming chamber and U.S. Pat. No. 3,337,322 to Taylor which describes a particular forming chamber gas mixture.
The present invention contemplates an improved means for the prevention of gas entry into forming chambers and may be appreciated from the following description.